The alley behind Nathan's house seems to be ""a place where something magic could happen,"" and ""one winter something did."" Pittman's (The Angel Tree) second winter fantasy of a friendship between a boy and a snowman is stunningly imagined by Col n (My Mama Had a Dancing Heart) in full-page and panel illustrations that possess the energy and narrative quality of an animated film. Cross-hatched etchings and scraped lines lend depth to the watercolor and pencil pictures, and Col n's creamy palette casts an amber glow of nostalgia over the slow-starting story. Nathan spends several nights observing the mysterious snowman's antics. One night, he offers the fellow some cookies, and the snowman rewards the boy with his life story and his friendship. Nathan, realizing the snowman will soon be moving north, decides to make him a mate so he won't be lonely. Col n characterizes the frosty fellow as a 1940s film star in a suave fedora, romancing his unexpected lady love until spring, when the couple must part for colder climes. Although the fanciful story is a bit thin, and the sentimental substance perhaps more appealing to adults than children, Col n's imaginative illustrations create a wintry, dreamlike atmosphere. Ages 4-8. (Sept.)